In that earlier invention a golf club is provided with at least one permanent magnet typically held in a bore at a non-impact surface. Various configurations are possible, but a generally useful configuration is to provide two magnets held in bores at the back of the club, near the sole and equally spaced to either side of the central plane of intended movement of the club head, i.e. as "heel" and "toe" magnets, with their axes "horizontal" and parallel to that plane.
This club is used in conjunction with one or more loops of electrically conductive material, and in use in passed over a length of such loop to give an electrical signal. Using such a linear pickup gives better sensitivity than the use of point magnetic sensors for the club head metal, as known in earlier prior art. As each magnet crosses the linear pickup a characteristic "zero-cross" signal is produced, with a number of measurable characteristics. The moment of cross-over relates to the zero value of this function. The symmetry of the zero-cross function is affected by tilt of the magnets, i.e. tilt of the club face in one or other direction. The shape of the zero-cross function is related to minimum distance of magnet from pickup, as it crosses, being thus a measure of height or (as difference of height between two magnets) a measure of rake of the shaft.
Use of a number of inductive loops of different shape and placements in relation to a designed ball position (such loops being for example fabricated into a suitable mat) can thus give a multiplicity of signals, of varying shapes, symmetries and delays, from which a processing unit can derive numerical values for angles (of loft, slice, hook or rake) speed, and displacements from an ideal path.